1. Field of the Invention
The present invention relates to radio frequency direction finding systems, and particularly to a single-antenna direction finding system for multi-rotor platforms.
2. Description of the Related Art
Radio frequency (RF) direction finding (DF) systems are used to detect the presence of a desired/undesired RF signal transmitter location. In early systems, this process involved mechanically rotating the directional antenna across the 360° azimuth plane to find the most probable direction of the RF transmission. If the transmitted signal duration is long enough, its position can be located quite accurately.
The majority of the initial RF DF antenna systems used multiple channel receiver systems, where every antenna element on the antenna array had a corresponding receiver. These systems were bulky and consumed too much power, and in some cases, were impractical due to mobility related issues. Recent advances in integrated chip (IC) and digital signal processing (DSP) technologies have given rise to small, portable, and highly versatile single channel DF systems. In order to accurately determine the position of the object in the far field of the antenna, it is desired to have a high gain (in the desired plane) and extremely narrow half-power beam widths (HPBW). Moreover, the scanning angle can be increased by modifying the geometry of the antenna array. Circular antenna arrays are an example of antenna arrays with a 360° scan angle. The selection of the antenna elements constituting the array is made on the basis of the individual radiation characteristics of the respective element types.
For high accuracy, we desire antenna elements that have narrow HPBW and high gains. Although several antenna array designs have been investigated in literature; none have actually been integrated within a multi-rotor UAV (Unmanned Aerial Vehicle) platform with a DF algorithm.
Thus, a single-antenna direction finding system for multi-rotor platforms solving the aforementioned problems is desired.